Wafer positioning system

Abstract

A wafer positioning system determines the position of a wafer during processing by monitoring the position of the wafer transport robot as the robot transports the wafer by one or more position sensors. The wafer positioning system incorporates a transparent cover on the surface of the wafer handling chamber and two optical position sensors disposed on the surface of the transparent cover. The position sensors direct light through the wafer handling chamber to reflectors near the floor of the chamber which reflect the light back to the position sensors. A detector within the position sensor detects when the beam path from the position sensor to the reflector is uninterrupted. As wafers are transported through the chamber, the edge of the transported wafer interrupts the position sensor beam path causing the output of the position sensor to switch states. When the position sensor output switches, the position of the wafer transport robot is measured. At least two data points are measured to establish the wafer position. If the wafer is not at its nominal position, the position of the wafer transport robot is adjusted to compensate for the wafer misalignment.

What is claimed is: 
     
       1. A wafer positioning system comprising: a wafer handling chamber, said wafer handling chamber having at least a portion of a wall formed from a substantially transparent material;   a wafer storage apparatus within said wafer handling chamber having a plurality of locations for storing wafers;   a wafer transport robot capable of translating a wafer along a first coordinate direction and along a second coordinate direction, said wafer transport robot having a blade adapted for carrying wafers; and   at least one position sensor comprising: a light source disposed external to said wafer handling chamber, said light source aligned to direct an incident beam of light through said substantially transparent material into said wafer handling chamber;   a reflector disposed within said wafer handling chamber so that at least a portion of said incident beam of light is reflected from said reflector as a reflected beam of light, wherein said reflector directs said reflected beam of light through said substantially transparent material; and   a detector disposed external to said wafer handling chamber to receive said reflected beam of light from said reflector, wherein said light source and said detector are disposed to detect an edge of said wafer when said wafer intercepts a beam of light as said wafer is transported from said wafer storage apparatus to a position within said wafer handling chamber disposed away from said wafer storage apparatus;     means for detecting a position of said wafer transport robot as said edge of said wafer intersects both a first detection position and a second detection position within said wafer handling chamber;   a converter which generates an interrupt signal; and   means for checking the state of said position sensor in response to said interrupt signal.   
     
     
       2. A wafer processing system of claim 1, wherein the converter is a servo motor controller to provide the interrupt signal to the means for checking the state of said position sensor. 
     
     
       3. A wafer processing system of claim 1, wherein the converter is a feedback device to provide the interrupt signal to the means for checking the state of said position sensor.